1. Field of the Invention
The present invention relates generally to a semiconductor integrated circuit, and is applied, for example, to a semiconductor integrated circuit including an electrically programmable fuse (e.g. eFuse).
2. Description of the Related Art
In the prior art, there is known a so-called MOS capacitor in which a source and a drain are mutually connected to implement a function of a capacitor. Use has been made of a semiconductor integrated circuit that includes a so-called antifuse element, wherein a high voltage is applied between the gate electrode and the source/drain of a MOS capacitor, thereby breaking a gate insulation film to let a current through, and programming the antifuse element (see, e.g. U.S. Pat. No. 6,667,902).
However, when data is read out after the antifuse element is programmed, the following situations (1) and (2) will arise.
(1) Read-Out Margin is Low.
The resistances of antifuse elements are randomly distributed. In general terms, there are a resistance value distribution of programmed elements and a resistance value distribution of non-programmed elements. When a read-out circuit is designed, these distributions have to be strictly examined and the programmed elements have to be distinguished from the non-programmed ones on the basis of a proper resistance determination value. However, the read-out circuit that determines the resistance determination value tends to be affected by an error in manufacture, and the read-out margin is low.
(2) The Test Time Increases.
The resistance value is a measure for judging how well programming is executed. To exactly measure the resistance value leads to an improvement in reliability. In an available method of measuring the resistance value, a current is fed through the antifuse element by a given selection means, and the actual current value is measured by a tester. In this case, about 50 msec, for instance, are needed to complete the measurement of the current that flows through one antifuse element. Accordingly, about 5 sec are needed to complete measurement for 100 programmed antifuse elements. Since such a long time is needed, the test time increases when a large number of resistance values are measured in mass-production.